


Experimental Mishaps

by Blackberreh



Category: Naruto
Genre: Alternate Universe - Canon Divergence, Established Relationship, M/M, Seal Shenanigans, Size Kink, Tentacle Sex, Tentacles
Language: English
Status: Completed
Published: 2019-03-27
Updated: 2019-03-26
Packaged: 2019-12-18 14:55:06
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 2
Words: 4,684
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18252128
Author URL: https://archiveofourown.org/users/Blackberreh/pseuds/Blackberreh
Summary: Tobirama fucked up with the new seals. This certainly was NOT what they were supposed to do.At least Madara is intrigued.





	1. Chapter 1

**Author's Note:**

> Here we have it, the long awaited TentaTobi fic that I've been teasing tumblr with for like, the past 2 months;;;
> 
> I hope y'all enjoy it x''D

The sensation was odd, Tobirama decided as he ran his fingers over one of the new appendages. A shiver worked its way down his spine and a slow, heavy heat began to curl in his gut, and Tobirama pulled his hand away quickly because he wasn’t sure if he was ready to tackle  _ that _ little problem yet. His digits were slick with a clear, odourless fluid, and he rubbed his fingers together for a few moments as his mind raced.

Of all the things the new seal was supposed to do, this… certainly wasn’t one of them. 

The tentacles - four of them, each sprouting from the expanse of his back - shivered and curled through the air around him. One twined around his thigh and another around his wrist, and Tobirama yanked it out of reach with a scowl, willing them to still. They did, thankfully, so it would appear that he at least had  _ some _ semblance of control over them. 

That was a small blessing at the very least. 

It was a little hard to think, however. His mind had grown hazy, the urge to keep touching the new appendages a thing that was growing rather tempting. He couldn’t see them very well from where they were connected to his back, but close to the base he could see red markings that he assumed came from the seal that had birthed them.

Absently, he brought his hand up to his mouth and licked at the fluid, deeming it as tasteless as it was odourless, and it remained slick, allowing his fingers to glide together without any sign of friction. Quite a decent lubricant, it would seem…

His thoughts were interrupted when a knock resounded on the door, and he felt a familiar chakra signature lurking outside - Tobirama startled, his new limbs jerking and knocking over a few empty glass bottles and an extra chair, sending them clattering to the floor, and the Senju let out a loud, emphatic curse.

He’d been so distracted he hadn’t felt Madara approaching at all!

The door shoved open without Tobirama’s approval and Madara slipped in, Sharingan activated and body tense. “Is everything alright? Are you-”

He froze and fell silent as he registered what he was actually seeing.

Tobirama half out of his chair, shirt hanging in tatters around him, looking flushed and unsteady as four white tentacles curled around the air about him. His red eyes were wide and unfocused as he looked at Madara, and his mouth opened and closed a few times before he grimaced and shifted to stand.   
  
“There has been an… incident.” Tobirama managed as he swayed unsteadily on his feet.

Madara’s gaze took him in, Sharingan flickering from his face, to the tentacles, to his bared chest and stomach, to the tentacles again, to his face - 

“An incident.” Madara replied, voice flat. His gloved hands twitched, as if he were going to reach for a weapon, but all he did was take a step closer.

Tobirama stumbled in his attempt to step back, and fell against one of the lab benches, hissing in pain as one of the tentacles was squished between the edge and his body. The tentacles shuddered and curled close around his body, draping across his shoulders and neck and waist and hips - and Tobirama squirmed at the odd duel sensations he could feel, and the odd slick the tentacles were producing that allowing them to glide across his skin. The new limbs were sensitive - very sensitive where they brushed against his body, and the sensation pooled in his gut.

Tobirama was beginning to have an inkling about what exactly was going on.

“Are they dangerous? Are you in pain?” Madara’s question brought Tobirama back out of his thoughts, and the Senju eyed him for a moment. Without his glasses he wasn’t able to fully discern the expression on his face, but he could see the red of his Sharingan flickering over his body - assessing him. 

“I am - unsure.” Tobirama bit out and willed the tentacles still once again. “They do not hurt, but they are… sensitive to touch. My back seems to be holding up under the added weight, but who knows if that will change over time.”   
  
One of the tentacles curled around his wrist, the others tightening their hold on his body, and Tobirama was hit with the sudden sensation of - comfort. Like he was crossing his arms over his chest, which he did when he was uncomfortable and trying to reassure himself. Hmm. 

Tobirama narrowed his eyes. Perhaps… they were more attuned to his body than he initially thought. 

He looked at the chair he’d knocked over, and one of the tentacles reached out and righted it with ease, and Tobirama tilted his head, eyebrows quirked in intrigue. “Mm. It appears they react to both conscious and subconscious thought. I do not…  _ think _ they are dangerous…”

Madara took another step closer, and Tobirama regarded him warily. He’d long gotten used to the other man invading his personal space, the sensation of his chakra a soothing presence on Tobirama’s frayed nerves, but in this current situation - he was still unsure if Madara was in any danger or not. The fluid the tentacles excreted appeared to be harmless to  _ Tobirama _ in the short term, but who knew how it could affect Madara?

“It would be best if you-” He was going to say ‘kept your distance’, but Madara had already reached out to touch one of the tentacles with a gloved hand - and the tentacle was stretching out on its own to curl around Madara’s wrist, pulling on Tobirama’s subconscious want for comfort. Tobirama squirmed, his eyes going wide. The tentacle curled further up the Uchiha’s arm, brushing against hot, hot skin, and Tobirama was hit with the sudden need to feel  _ more  _ of that heat-

He took a step forward before he realised, and used all of his willpower to hold himself still, trying to stop his shivers. The tentacles squirmed, but remained where they were, draped about his body, save for the one that was steadily trying to creep up Madara’s sleeve and get more of that warmth. 

“Huh.” Tobirama’s gaze snapped up to Madara’s face. He was close enough to see his expression properly now, and the Uchiha looked - confused. A little concerned. Intrigued. “It’s warm. And… slippery.”   
  


“Apologies.” Tobirama grimaced and tried to get it to release Madara, but the Uchiha was already moving. He pulled the glove off his free hand with his teeth and reached out to touch the tentacle with bare fingers, and Tobirama suddenly found himself enraptured by the curiosity that enveloped Madara’s expression.   
  
“It’s really smooth.” The Uchiha murmured, rubbing his fingers gently over the length curled around his wrist. “And this-”   
  
He pulled his hand away, much to Tobirama’s disappointment, and brought his fingers up to his face - taking in the slick that coated his digits. “Lubricant?”

Tobirama tensed up, a sudden stab of arousal hitting his gut as that word brought forth some very, very interesting images to mind. “It would - seem so. It doesn’t have a taste or scent either. I believe it’s harmless, but I can’t be certain unless I t- te-”   
  
Tobirama trailed off with a stutter, heat suffusing his cheeks as he watched Madara lick the slick off his fingers in an unintentionally erotic display. Madara continued to stare down at his fingers, brow creased in thought, and Tobirama couldn’t help taking another step closer and crossing that small distance between them. 

At that, Madara looked up, an eyebrow quirked in question, and Tobirama swallowed thickly. He wanted to press himself against the elder man, wrap his limbs around him and soak up the heat of his body. He pursed his lips and let out a shuddering breath. “I believe it is… affecting me in ways beyond simple body modification.”

“‘Simple body modification’?” Madara repeated dryly, though his voice took on a slightly breathy tone. “Would you care to explain?”

Tobirama licked his lips, eyes fixated on Madara’s mouth. “Ah. I am… I feel hot. My body. You touching them, ah… It feels-” The flush on Tobirama’s cheeks darkened. He was not usually this…  _ shy _ about sexual activities, but this was simply… new. “It feels sensitive. It could be because they are newly created and sensitivity will… fade in time, or... I believe they could be new erogenous zones.”

Madara’s brows shot up at that and he blinked rapidly. He had some colour to his cheeks now as well, his fingers absently stroking the length still curled around his wrist. “Is… that so?”   
  
Tobirama cleared his throat. Another one of his tentacles snaked out and lightly curled around Madara’s waist, and his eyes snapped to the pale white limb. The fluid left dark streaks on his robe, but Madara seemed to not care as he let out a shuddering breath. He then licked his lips, and Tobirama’s eyes tracked its motion with growing hunger.

“So,” Madara began, his voice deepened to a rumble. “You could say that right now, you’re…” His eyes flickered down Tobirama’s body - his bared chest and stomach, and very obviously tented pants. “You’re aroused?”

“Obviously.” Tobirama managed to get out. He squirmed a little and brought a hand up to tug at the scraps of his shirt, pulling it off. Madara watched with darkening eyes. “It has been getting - progressively worse as the minutes pass.”

“Ah.” Madara’s cheeks flushed brighter, and his breathing had picked up. Tobirama noted that down distantly, red eyes flickering to the hand  _ still _ stroking the tentacle around Madara’s wrist. “Well. Would you - would you like my assistance?”

Tobirama froze. His mouth went dry, and he looked at Madara with large eyes. He sucked in a harsh breath through his nose, and ground out, “Are you certain?”

Madara’s eyes narrowed on him, face pulled into something that could be called a pout. “ _ Yes _ . I wouldn’t have asked if I wasn’t-”

He was cut off when Tobirama abruptly tightened the tentacle around his waist and tugged the elder man flush against him. Madara let out a strangled noise, eyes going wide and mouth opening up to say - something, but Tobirama didn’t let him get started. He ducked down and drew the Uchiha into a biting kiss, his movements bordering on just a little too forceful, but Madara kissed back with equal ferocity once he’d gotten over his shock. The tentacles moved with barely a thought, all of them finding some part of Madara to latch on, and the tip of one attempted to squirm underneath the elder man’s robe.

Tobirama pulled back after one last lick and Madara squirmed in his grip - very much bound. Two tentacles wound around his arms, one around his waist, the other curling around a strong thigh beneath his robe - creeping closer and closer to his groin. Madara was panting, face now fully red and eyes glazing over, and Tobirama’s eyes narrowed. Generally, a kiss and some petting was hardly enough to get Madara this aroused. So it was a little odd that-

Ah. The fluid.   
  
Tobirama shivered and leaned in to nip at Madara’s jaw, his hands moving to undo the elder man’s robe. Madara had both touched and ingested the fluid, as had Tobirama. He should have run it through some tests before anything like this even began to ensure it was safe, but…

It must act as some kind of aphrodisiac.

It was getting harder and harder to think. Arousal was burning hot and heavy in his gut, and with a frustrated noise, one of the tentacles promptly tore the fabric of Madara's robe, leaving him in just his pants and undershirt.

Madara squawked. A loud, high pitched sound that had amusement mingling with the arousal and caused something light to bubble in his chest, and Tobirama leaned in to lick at the pale column of his neck that was now exposed. His lips traced up to Madara’s pulse point, feeling the way it fluttered fast against his lips, and gave a pleased hum. Pressing flush against the elder man, chest to chest and groin to groin, and Tobirama would be lying to himself if he wasn’t… enjoying how already affected Madara was. The hard heat he could feel against his own made him want to purr.

“I don’t think - that was necessary.” Madara said haltingly. “You could have just let me undress.”   
  
“Mmm.” Tobirama ran his hands down Madara’s sides - paused at the edge of his shirt and fiddled with the hem. “It was in the way. So are these.”

Madara’s eyes only had time to narrow before the tentacle around his waist pulled and tugged - releasing Madara’s arms to help tear it off. The Uchiha let out another noise of protest, but Tobirama silenced him with a kiss, gripping his face with his hands and licking into his mouth, swallowing his groan. The tentacles resumed their hold - two around Madara’s arms, sliding up to loop around his shoulders, and the other curling tightly around a thigh - the slender tip absently playing with the hem of his pants, frustratingly close to that trapped, hard length.

Madara let out a frustrated noise against Tobirama’s mouth, and he pulled back to scowl at him, colour high on his cheeks. “Are you going to get on with it or are you just going to spend the next hour teasing me.”

Tobirama’s lips curled into a small smirk, and the tentacle slipped into his pants - causing Madara to jerk and gasp as it curled tightly around the base of his cock. He was out of breath and it was a little hard to articulate, but he managed “As much as I would enjoy that… I am, admittedly, starting to get - impatient.”

A breathy laugh escaped Madara, ending in a groan as Tobirama ever so carefully tightened the tentacle and had it curl up his cock - and promptly shoved Madara’s pants down his thighs, revealing the sight to Tobirama’s hungry eyes. The pale tendril stood out against the flushed skin, pink tip already beading with precum, and Tobirama licked his lips.

“Well?” Madara ground out, hips twitching in an attempt to thrust into the tentacle’s hold, but the greater bulk of the limb was easily managed to keep him still. “Are you j-just - just going to stare at it or actually  _ do _ something about it?”

Tobirama’s eyes flickered up to meet Madara’s. The tentacle around his shoulders had tightened a little, now curling more around his neck, and he realised vaguely that it would be so easy to tighten it. To cut off his breathing. In the past, when they were still antagonistic towards each other, Tobirama wouldn’t have hesitated - to shut Madara up, to threaten; but now… 

He wondered what would happen if…

Madara registered the tentacle tightening and his mouth fell open a little, eyes meeting Tobirama’s. Holding his gaze, Tobirama had it curl tighter and tighter, looping around several times, waiting for Madara to say something -  _ anything _ \- in protest. But Madara’s eyes held nothing but trust, and Tobirama’s mouth went dry.

These tentacles held so much strength. Like this, he could likely do some serious damage if he so wished. Maybe even kill. Just an easy jerk, and bone would snap. 

But this - this wasn’t the time for such thoughts. The trust Madara was showing him… Tobirama was loathe to even think about breaking that. Now, he just wanted to see just… what sort of noises he could wring from Madara. To see him gasp for air and writhe in pleasure as - 

Oh.

These tentacles had a lot of strength…

Tobirama licked his lips, and Madara yelped as his arms were released - and he was promptly lifted into the air and placed to sit on an empty workbench. A tentacle wrenched his thighs open, his arms were pulled behind his back and bound together, and Tobirama pressed up flush against him, placing his hands on Madara's heaving chest. Madara's eyes were wide, pupils dilated, lips parted as he panted for breath, and Tobirama couldn't stop himself from leaning in and biting that spit slick bottom lip.

Madara moaned and shuddered against him, arching as Tobirama raked his nails down his chest, leaving red marks across the pale expanse.

Madara had few scars. A testament to his battle prowess, and Tobirama adored leaving all sorts of marks over that pale, unmarred skin. The Uchiha never seemed to protest - in fact, he seemed rather vocal about the attentions. He released Madara's lip and scraped his teeth down the column of his neck, wasting no time in biting and licking and sucking that bare skin, leaving blossoming red marks in his wake.

Madara squirmed and cursed, struggling against the tentacles holding him still but to no avail. Tobirama held him firm, and the Senju had to struggle at keeping the savage grin from his lips. 

Madara was starting to sound desperate. This was a nice role reversal. Usually, it was Tobirama that was held down, please forced from his lips as Madara brought him to heights that he never would have even imagined reaching a few years ago.

Tobirama was going to savour this.

He scraped his teeth down Madara's chest and bit down on a nipple, hard. The Uchiha bucked up against him, a whine escaping his lips, but Tobirama didn't let up. He nibbled and sucked until it was peaked and aching, ignoring the way Madara's curses began to take on a desperate edge. Keeping this up would be fun - he rather would like to see if he can get Madara to beg just from this - but truthfully, Tobirama was getting rather desperate himself.

So he moved on. Scratched a nail over his other nipple, and lowered himself down to his knees, bringing himself eye level with Madara’s hard, throbbing cock.

Tobirama licked his lips, and looked up at Madara. His lover's face was flushed, his eyes now a spinning mixture of red and black, and Tobirama felt a shiver crawl down his spine. Having those Sharingan eyes always used to unnerve him, but the more time they spent together, the more they fucked, the more the idea of this - of Madara memorizing these activities - appealed to him. Filled him with lust.

Tobirama groaned and gripped Madara's thighs. A conscious thought had the tentacles loosening and slipping away, leaving thick trails of slick in their wake. He couldn't be sure, but he thought that maybe they were excreting more of it due to the arousal? A thought to be filed away for later. 

He ducked down and licked a hot stripe up the base of Madara's cock and ran his fingers through the slick coating his thighs. Madara threw his head back with a groan, and - Tobirama didn't want that.

A tentacle slipped around Madara's neck, tugging - choking him ever so slightly. Madara's eyes flew open with a strangled noise, his mouth hanging open, slack, and Tobirama commanded, “I want you to keep your eyes on me.”

Madara started, eyes wide and uncomprehending. Tobirama's eyes narrowed, and he gently tightened the tentacle around his neck.

He knew very well of this kink of Madara's. Tobirama had come to appreciate it quite thoroughly, but this was on a whole new level. If the way Madara's cock twitched and he strained for some sort of stimulation was any indication, a wheezing curse escaping his lips, then yes - Madara appreciated it quite a bit as well.

“Do you understand me, Madara?” Tobirama gripped his cock with a slick hand and gave it a hard stroke, causing the Uchiha to whimper. “Eyes on me. Do not move them.”

Madara tried to nod, but with his neck held as it was the motion came out jerky - and he probably succeeded in choking himself further. He blurted out, “Y-yes - fuck, I won't look away, just - fucking - Tobirama-”

Tobirama hummed his approval and then ducked back down to suck the head of Madara's cock into his mouth. The Uchiha jerked and groaned, but when Tobirama looked up he was doing as instructed, eyes fixated wonderingly on Tobirama - and the Senju shivered at the feeling of having those intense eyes on him.

He hummed his approval, working his mouth slowly down Madara's cock, and reached down with the slick fingers of his free hand to gently prod at Madara's entrance.

He saw those eyes widen, his mouth open to emit nothing more than a gasp as Tobirama slipped a finger in with ease. Another thing Tobirama noted absently - there was very little resistance. Did the slick have a relaxing effect as well as an aphrodisiac? Another thing to be examined later.

He wiggled that finger around as he worked on taking more of Madara's cock into his mouth, relishing in the choked noises his lover was emitting. He slipped in another finger, and again was met with hardly any resistances, and he carefully kept an eye on Madara's face for any sign of discomfort.

Absolutely none, as far as he could tell. Chest heaving as he sucked in fast breaths, drool dripping down his chin, eyes distant but still fixated on Tobirama below him -

It was perfect. Utterly perfect. Tobirama wished he had the visual prowess to memorise such a sight.

He slipped in a third finger and grazed them across Madara's prostate, delighting in the way his passage tightened around his fingers and Madara's  eyes fluttered shut.

Couldn't have that now.

He tightened the tentacle around his throat and mercilessly scraped his fingers over that spot deep within him, and Madara's eyes flew open with a cry.

He pulled off Madara's cock with a wet pop and withdrew his fingers - dragging another cry from his lover - and moved to stand once more between Madara's spread, quivering thighs.

“Eyes on me.” Tobirama murmured again, and relaxed the hold on Madara's neck. The uchiha sucked in greedy lungfuls of air, face flushed bright red, expression dazed and desperate, and Tobirama couldn't help but lean in for a sloppy, entirely uncoordinated kiss. He held Madara's gaze the entire time, enraptured by the way the blown out pupil nearly overtook the red of the Sharingan. He placed his slick hands on Madara's waist, brushing his own hardened - still clothed cock up against the Uchiha's, and moved one eager tentacle into to position.

Whatever concentration Madara was able to hold onto was blown out the window and he stopped kissing all together as the tentacle eased its way inside at an easy glide.

The tip was thin and tapered. It wouldn't have had much trouble at all if Tobirama hadn't stretched Madara already. Maybe that could be something to play around with later.

But after an inch or so, the tentacle became thicker, and Tobirama fed it in with hunger, the sensation of something so hot and tight squeezing around it so arousing that he couldn't help grinding his cock against Madara's. Madara moaned, low and desperate, and Tobirama continued to push it in, more and more, stretching out Madara more than he likely ever had been before.

The thought had Tobirama pressing in  _ even more _ , lust and desire pooling in his gut. Madara's mouth fell open in a soundless cry, and Tobirama smoothed his hands gently up and down his lovers sides, watching his expression with hungry eyes.

“Is it too much?” He murmured. Directed the last remaining tentacle to curl back around Madara’s thigh, the thinner tip curling tightly around the base of Madara’s cock. Madara shuddered and tried to buck, but to no avail. He looked so unfocused, tears leaking from the corners of his eyes, mouth twitching and gasping -

“M-more-” He said, voice ragged and desperate.

Tobirama’s lips pulled into a smirk before he could help himself, and he reached up to gently wipe away the trail of drool from the corner of Madara’s mouth. “I’ve never seen you pull this kind of face before, Madara…”

The Uchiha leaned into his touch with a needy moan. Tobirama pressed his thumb to his bottom lip and Madara licked at it on instinct, eyes wide and desperate, and Tobirama’s breath caught in his throat.

“How lewd.” He murmured. “I wonder… can I make you scream?”

Barely a thought passed Tobirama's mind when the tentacle pressing into Madara shifted, curled, and pulled back out at a slow drag - making sure to rub against Madara's prostate as it went, and Tobirama relished in the whine. The tentacle around the Uchiha's cock tightened, preventing him from cumming - and then the tentacle abruptly thrust back in, hard and fast and so much deeper than before-

Madara screamed, and it was one of the most delightful things Tobirama had ever heard. He rubbed soothingly at Madara's sides, absently grinding up against him, wanting to cum but also wanting to prolong this for as long as possible. The tentacle thrust again and again, and Madara fought against his bindings, sobbing in pleasure, in desperation - there was so much of that tentacle stuffed into Madara at the angle he was at now, Tobirama could feel the movement from where his belly and cock were pressed flush against Madara, and Tobirama groaned and dug his nails into Madara's skin, directing the tentacle to thrust harder,  _ faster- _

“Please -" Madara choked out. “Please - please, I need - I need to cum, p-please Tobi plesse-”

Sage but Tobirama needed it too. And Madara was begging - actually  _ begging _ , something that he had never heard the Uchiha do before and the noise went straight to Tobirama's cock. Before he realised, Tobirama released the tendril from around the base of Madara's cock, and had it wrap around both Madara's and his. It was hot and slick and Tobirama bucked against Madara with a low curse, the tentacle within Madara picking up speed-

And then Madara was arching, crying out again, voice hoarse and cracking from the strain. His release painted their stomachs white, made the tentacles movements even more slick. His passage rippled around the tentacle and the pleasurable sensation crawled right up Tobirama's spine and then he was cumming as well, grinding against Madara and biting down on his collarbone to muffle his cry. The tendril around their cocks continued to milk them - almost to the point of oversensitivity, and Tobirama only stopped when Madara let out a groan of discomfort.

Breathing heavily, mind dazed and vision foggy, Tobirama gently relaxed the hold he had on Madara. He released the Uchiha's arms and they flopped down to rest against the bench, boneless and shaking from the strain and aftershocks of pleasure. That - wasn't good, Tobirama registered distantly, he needed to see that his arms were alright, that the blood was flowing properly again. The tentacle around Madara's neck slipped off and curled around his arms and shoulders, rubbing gently, and Tobirama rested his forehead against Madara's heaving chest and just -

Breathed.

He wasn't really aware of how long it was before he truly came back to himself. He remembered moving in a daze, Madara jerking and whimpering as the tentacle was eased from his ass, bringing with it a gush of the lubricant. He wrapped his arms around Madara's waist and somehow ended up on the floor, the Uchiha boneless in his lap and flush against his chest, with his mass of hair getting in Tobirama's face and the tentacles draped around various parts of their body in a warm, slippery embrace.

It was both the most comfortable, yet odd position Tobirama had ever found himself in.

He wasn't going to complain. Madara wasn't either, if the way he let out a sleepy mumble and snuggled further into the embrace was any indication. Tobirama knew that they should probably… move. Clean up. Talk about what had just happened. Work out what the hell should… or rather  _ could _ be done about the tentacles. And the fluid. And they should… also test it properly. Just to - just to double check that it was truly safe.

But tobirama was comfortable. Madara was comfortable. All of that could come later. Maybe.

For now they could just… rest.

 


	2. Chapter 2

**Notes for the Chapter:**

> Here we just have some smutty pictures lol

**Author's Note:**

> AAAH I hope you guys liked it;;; lemme know what you think ;v;/
> 
> Next chapter is just. Smutty art lol


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